The present invention generally relates to semiconductor packaging, and in particular to a system and method for solder plating lead frames.
A common integrated circuit (xe2x80x9cICxe2x80x9d) package type has the IC die encapsulated in plastic with external metal leads. The packaging process begins by placing the IC die on an island of a metal lead frame. FIG. 2 illustrates a typical lead frame 100 with islands 110. The IC die is connected to leads 120, with soldered wires for example. At this stage of the process, leads 120 are connected by dambars 130. To encapsulate the die, two halves of a plastic mold are placed around the IC die and the mold is filled with liquid plastic. As illustrated in FIG. 3, dambars 130 retain liquid plastic 140 within the mold 150. The plastic 160 that forms between the leads 120 next to the dambars 130 is referred to as xe2x80x9cflash.xe2x80x9d After the plastic solidifies, the mold is taken away and the dambars and flash are removed.
To facilitate soldering of the leads, the metal lead frames are solder plated, usually prior to forming the IC package. After solder plating, lead frames are rinsed with hot de-ionized water. Poorly rinsed lead frames have discoloring due to acid contamination and other impurities, which are potential causes of corrosion and failure to pass solderability testing.
Solder plating machines commonly employed include a de-ionized water rinse to remove acid contamination and other impurities. However, parts such as lead frames are sometimes poorly rinsed due to problems in the de-ionized water supply, which causes a loss of material or expensive reworking. Problems with the de-ionized water supply are manifest by fluctuations, decrease, or loss of de-ionized water supply pressure and produce interruptions or variations in the flow of de-ionized water against the parts being rinsed.
It is known to provide a solder plating machine with a de-ionized water pressure gauge and to institute periodic inspection of that gauge. The gauge and inspection process sometimes leads to the discovery of problems in the de-ionized water supply. Nonetheless, there remains an unsatisfied need for a solder plating machine and method that reduces the occurrence of poorly rinsed lead frames.
The present invention provides a solder plating system with automatic monitoring of wash fluid pressure. The system automatically activates an alarm and/or initiates shutdown of a solder plating machine when the pressure reading indicates a failure of the wash fluid supply. The system thereby reduces the number of parts that are affected by failures in the wash fluid supply system. In some cases, problems with the wash fluid supply are detected before any parts are affected.
One aspect of the invention relates to a solder plating system comprising a solder plating machine, a wash fluid supply system for supplying wash fluid to the solder plating machine, a pressure sensor for monitoring the pressure of wash fluid supplied by the wash fluid supply system, and a switch control system for automatically switching an alarm based on one or more readings supplied by the pressure sensor.
Another aspect of the invention relates to a solder plating system comprising a solder plating machine, a wash fluid supply system for supplying wash fluid to the solder plating machine, means for monitoring a pressure of the wash fluid supplied by the wash fluid supply system, and means for triggering an alarm when the wash fluid pressure varies outside preset parameters.
A further aspect of the invention relates to a method of operating a solder plating system comprising supplying wash fluid for a solder plating machine, obtaining pressure readings for the wash fluid supplied to the solder plating machine, and automatically activating an alarm based on one or more of the readings.
A further aspect of the invention relates to a method of operating a solder plating system comprising supplying wash fluid for the solder plating machine, obtaining readings relating to a pressure for the wash fluid supplied to the solder plating machine, and automatically shutting down the solder plating machine based on one or more of the readings.